1. Field of the Invention
The present invention relates to autofocus technology in image capturing apparatuses.
2. Description of the Related Art
Digital still cameras and digital video cameras are examples of image capturing apparatuses that employ an image sensor capable of photo-electric conversion such as a CCD or CMOS sensor. In these cameras, system simplification, reduced cost, and reduced size are realized by using an image sensor used to capture a still image or a moving image as a focus detection sensor, without having a separate sensor for focus detection.
In the case of a configuration in which an image sensor for capturing is used as a focus detection sensor, ordinarily a television AF system is adopted in which a lens position that is in focus is searched for from a frequency component of data that is read out from the image sensor. In this system, an image processing circuit is used to extract the frequency component from the image data read out from the image sensor, and the region extracted can be set as desired depending on the specifications of the image processing circuit.
When capturing a still image or a moving image with a camera, it is assumed that the photographer will capture the image by operating the camera such that a main object is in the center of the frame. Ordinarily, in the AF operation, the frequency component extraction region as well as the focus detection region are set such that focus detection is performed near the center of the frame. However, a case is also conceivable in which the capturing intent of the photographer is not limited to arranging the main object in the center of the frame, but rather the photographer intends to capture an image with the main object arranged at the edge of the frame. In order to respond to such needs, a camera has been proposed that has a focus detection mode in which the focus detection region is fixed in the center of the frame, and a mode in which it is possible to move the focus detection region to a desired position (see Japanese Patent Laid-Open No. H7-283994).
Also, a user interface has been proposed in which, in a camera provided with a plurality of focus detection modes as in Japanese Patent Laid-Open No. H7-283994, it is possible to simply switch the focus detection mode and select the focus detection region (see Japanese Patent Laid-Open No. 2006-39203). Conventionally, there have been cameras provided with a focus detection mode in which the focus detection region is fixed near the center, and a focus detection mode in which the focus detection region is arranged at a desired position. On the other hand, in order to respond to a wider range of user needs, cameras are desired that are provided with a plurality of focus detection modes in which the focus detection region can be arranged at a desired position. However in this case, it has been assumed that issues will arise with respect to storing position information and size information of the focus detection region selected by the user.
For example, assume that in a focus detection mode A, capturing is performed after arranging the position of the focus detection region at the left edge of the frame such that the focus detection position becomes optimal for a particular image capturing condition. Next, assume that in a focus detection mode B, capturing is desired after arranging the position of the focus detection region at the right edge of the frame such that the focus detection position becomes optimal for another image capturing condition. At this time, the position of the focus detection region designated in the focus detection mode A is also reflected in the focus detection mode B, and thus optimal focus detection region information for differing image capturing conditions is not generated, which is disadvantageous for the user.
Also, when a plurality of AF frames have been set, the display becomes confusing if all of the AF frames are always displayed in the viewfinder frame, so that it also becomes difficult to confirm the object in the viewfinder frame. It becomes more difficult to see the object as the number of AF frames increases. However, the position of a focus adjustment region cannot be confirmed if the AF frames are not displayed.